Weld control system with current compensation



Jan. 6, 1948. H. D. VAN SCIVER, 2D 2,434,132

WELD CONTROL SYSTEM WITH CURRENT COMPENSATION Filed May 23, 1944 [93 1 WELD IL CONTROL 20 r 9 92 ,8?

STARTING 8 Y B r---- Harem I E g i 21 24 21 l I 1 Z3 86 85 POWER I POWER 62 88 CONTROL CONTROL 55 0 O H 0 O 0 [83 4s 22 22 19 7 8 INVENTOR HERBERT DOANE VAN SCIVERII A TTORNE Y Patented Jan. 6, 1948 2,434,132

UNITED STATES PATENT OFFICE WELD CONTROL SYSTEM WITH CURRENT COMPENSATION Herbert Doane Van Solver, II, Merion, Pa., as-

;ignor to The Budd Company, Philadelphia,

a corporation of Pennsylvania 6 Claims. 1

This invention relates to an electrical system for controlling a weld and for automatically compensating for variations in current supplied to the weld.

In my copending application, Serial No. 524,243,

2 heat control units generally designated by numeral 20, as well as the ignitrons l8 and is. These ignitrons which are of conventional construction, including an anode 2|, cathode 22, and igniter 23,

within a gas filled chamber and the anode of each filed February 28, 1944, I have described a weld tube is connected to the cathode of the other control system in which utilization is made of the tube, the cathode of tube l9 having connection change of voltage occurring during the period to the transformer primary II and the cathode of weld at the weld point for establishing a conof tube l8 having connection to the source tertrol of the welding circuit as by opening the cir- 10 minal H. The igniters are each connected to cuit when the weld is complete. By this system power control circuits of conventional arrangeit is possible to supply welding current to the ment as well as to the control circuits for starting workpiece continuously and without utilization of time and heating as utilized in the usual form of accessory timing means which will automatically synchronous resistance welding. The initiating open the circuit as soon as the metal becomes switch 24 is indicated as associated with the startfused at the weld point and the weld is completed. ing time and heat control circuits.

In such control system, however, inaccurate re- The C, or amplifying unit, is illustrated as havsults may arise due to the fact that there may be ing direct connection to the electrodes I3 and i4 variation in source line voltage, in load current, of the welding equipment. Asshown, the primary in operation of the various electronic or relay de- 30 of an impedance matching transformer 3i is vices, or in other circuit apparatus which will connected at either end to one of the electrodes, tend to cause a momentary but undesirable the point of attachment being such as to obtain change in the current flow through the primary in effect the voltage drop across the workpiece at of the welding transformer and which will be the weld point. The secondary 32 of the transeifective in the weld control circuit and register former 3| is connected in series with a resistor improperly in the indicating or operating devices 33 which serves as a potentiometer for a sliding of the system. contact 34 having connection to the grid 35 of an It is an outstanding object of the present invenamplifying vacuum tube 36 so that variation of tion to provide, in weld control apparatus, circuit grid potential of the tube may be readily effected means for compensating for effects of variations by shifting the slider 34 along the resistor 33. in the current flowing in the welding circuit. Tube 36 includes also the cathode 31 connected Other related objects will appear on considerato ground through a biasing resistor and capaction of the following description of a preferred itor 38 and 39, and an anode 40 connected directly embodiment of y invention together with the to the primary M of a coupling transformer 42. d wi illustrating diagrammatically a Wi n The primary 4| also has connection through a diagram of this system. source of positive potential 43 to ground.

Referring to the drawing, there is indicated The secondary 44 of the coupling transformer therein a circuit arrangement having component 42 may be directly connected to the weld control parts indicated by the capital letters A, B, C, D, circuit E but if so connected without any interand E, respectively, and denoting the welding vening control apparatus it would fail to make transformer, the welding transformer control correction or compensation for current variation unit, the weld voltage amplifying unit, the current in the primary of the welding transformer circuit. compensating unit, and the weld control circuit. Accordingly, I have found it important to utilize The welding transformer circuit includes the the D circuit in association with the amplifying transformer I0 having a primary H and sec- 45 circuit C so that the two circuits in combination ondary l2. The secondary of the transformer is deliver to the weld control circuit a signal develconnected to the electrodes l3 and I4 which are oped at the weld point on completion of weld a pted to include and compress etween them which is correct as regards its relation with a the workpiece IS. The primary ll of the welding voltage drop at the weld point. This current transformer l 0 at one end is connected to a power compensating circuit D comprises a current transsource terminal l6 for alternating current and former 50 in electrical association with the prithe other end is connected to the associated power mary circuit 5| intermediate the welding transsource terminal l'l through inversely connected former II and the control unit B, the secondary ignitrons l8 and IS in the 13 unit of the system. 52 thereof being in series with a resistor 53. One The B unit includes the starting, timing and 55 end of the resistor has connection through the primary 54 of a phase inverting transformer 55 to a contact slide 58 engaging the resistor 58.

The secondary of the phase inverting transformer 55 includes two coils 51 and 58 which may be connected to the circuit including the secondmy 44 of the coupling transformer 42 and also a resistor functioning as a potentiometer or voltage divider 58 and thermionic vacuum tubes 50 and I! connected so as to pass current through the voltage divider on successive alternate half-cycles of the current transmitted from the current transformer 58. The coils 51 and 58 are wound in opposite sense so as to produce a phase change of 180 in transmitted impulse. In the specific adaptation shown, the ends 82 of secondary 51 is connected to the grid 63 of tube 8i and .the end 54 of the secondary 51 is connected to the anode 85 of tube 80 and to the voltage divider 58. Similarly, the end 85 of secondary 58 is connected to the grid 81 of tube 50 while the end 88 of this coil is connected to the anode 89 of tube BI and to the other end of the voltage divider 59 through secondary H of transformer 42. Also, cathode ll of tube 60 has connection to the point 88 of secondary 58 through the biasing resistor 12 and capacitor I3 and the cathode H of tube 6! has connection to the point 64 of secondary coil 51 through biasing resistor 15 and capacitor 18.

The E unit of the system is adapted to receive current from the voltage divider 59 between points 80 at one end of the divider and slidable contact 8|, this voltage being impressed across the primary 82 of amplifying transformer 83, the secondary 84 of which has connection through rectifying tubes 85 and 86 to the positive side of a conductor 81 in the E circuit. The negative side leads from the mid-point 88 of the transformer secondary 84 to the negative conductor 89 of the E circuit. Suitable filtering means 90 are utilized to smooth out the rectified current. From the rectifying apparatus the circuit is led through the capacitor 9i and rectifying tube 82 and the voltage drop across the tube 92 is passed through a suitable translating circuit, indicated as the weld control 83, to the starting, timing and heat control circuits 20 where the appropriate relay or other apparatus is energized to open the welding circuit.

The operation of the circuit to accomplish the objects of the invention may now be detailed. The workpiece i having been positioned between the electrodes i3 and I4 and compressed thereby through the usual mechanism available in resistance welding apparatus, source current is made efiective at the terminals l6 and IT to place the power controls in condition for operation. The initiating switch is then closed, thus activating the starting, timing and heat control and power control sections of the circuit to bring about a flow of welding current through the primary and secondary of the transformer l8 and thus through the welding electrodes i3 and I. The welding current in passing through the workpiece heats the same, particularly at the interface of the plates, as shown, to produce a nugget of molten metal.

Prior to the development of the fused area, a definite potential drop occurs across the workpiece which is transferred through the C amplifying unit to voltage divider 59 in the D and E circuits. There is thus impressed across the voltage divider, between the point 88 and slide 8!, a voltage drop which is related directly to the voltage drop between the electrodes. Should the weld now be completed. the resistance at the interface of the workpiece drops and a new value of potential develops across the eelctrodes which is made effective between points and 8| of the voltage divider 58. This change of potential is made effective on the comparator unit E which functions to energize an indicator or to open the welding circuit; but simultaneously with the development of the signal there may occur a current variation in the primary oi the welding circuit which will upset the accuracy of the indication or prevent the proper operation of the control mechanism. Should this fortuitous current change occur in the welding primary circuit, it is at once made apparent in the current transformer 50 of the D circuit and, depending on whether or not the half-cycle is positive or negative, will be translated to the grid of either tube 88 or ll of this circuit. Assuming the tube 88 as active in passing a positive half-cycle of current and assuming that a voltage drop occurs in the primary welding circuit resulting in a diminution of current flow, the construction and connections of the secondary 58 of the transformer 55 is such as to produce an increment of positive potential on the grid 81 whereby current through the tube 88 is increased. This causes an increase of current flow in the voltage divider 58 from points 88 to 8! thus increasing the voltage drop and automatically compensating for the voltage'drop occurring between the electrodes in the workpiece and made effective at the voltage divid" 58 through the transformer 42. It is thus apparent that irrespective of chance variations in the current in the primary welding circuit, the potential drop made effective in the voltage divider 58 relates only to that occurring between the electrodes and hence a correct and uniform signal is transmitted to the comparator circuit E.

As previously mentioned, circuit E is effective to develop the initial voltage across the electrodes prior to the breakdown of the metal at the interface of the workpiece and this is accomplished through the capacitor 9| which assumes the maximum initial voltage and which, after the voltage drop at the weld point due to completion of the weld, discharges through the weld control 83 to set in motion the apparatus in the starting controls 20 to bring about an opening of the welding circuit or to afford an indication of the completion of a successful weld.

It is apparent that the circuit, as disclosed, includes only the essential branch circuits and apparatus necessary for accomplishing the objects of the invention. Refinements may be made such. for example, as inclusion of additional apparatus for removing ripples from the circuit rectified through transformer 83 in the E circuit. Various other modifications may be made in accomplishing the main result of the invention, namely, to compensate for chance variations in the weld current during the time a weld is taking place.

What is claimed is:

1. In combination a power source, a load circuit connected to said power source, a resistor, translating means between said load circuit and said resistor, and compensating means connected between said power source and resistor eflective to compensate in said resistor for chance variations in current in said load circuit, said compensating means comprising a current transformer connected to said power circuit, a phase inverting transformer connected to said current transformer having a dual coil secondary, two electronic tubes having anode, grid and cathode elements and each connected in reverse parallel across said resistor and conductors connecting the anode and grid of each tube to separate dual coil secondaries whereby changes of current flow in said resistor due to current changes external to said load are compensated.

2. A current compensating system comprising a power source, a load circuit connected to said power source, a resistor, translating means between said load circuit and resistor, and current compensating means between said load circuit and said resistor effective to compensate in said resistor for current variations in said load circuit, and control means connected to said resistor, said current compensating means comprising a current transformer electrically relatedto the power source, a transformer connected to said current transformer having dual secondary coils, two vacuum tubes connected in reverse parallel with reference to the resistor, each tube having a grid connected to one of said coils and an anode connected to the other of said coils, the grids being connected to separate coils and the cathode of each tube having attachment to the anode of the other tube whereby said tubes alternately pass currentin successive half-cycles of alternating current flow, the phase relationship of the grids of said tubes being such as to increase the current flow through the resistor on decrease of power circuit current and to decrease the resistor current on increase of power circuit current.

3. In combination, an electric power source, a load circuit connected to said power source, means for applying power impulses to said load circuit, voltage responsive means connected to said load circuit dependent on load voltage change for terminating said power impulses, and means for additionally controlling said voltage responsive means in response to current variation in said load circuit during the time of transmission of said power impulses.

4. In combination, a power source, a load cirzuit including a load connected to said power source, means for applying power to said load cirzuit and load, control means for power mechmism connested to said load circuit at said load idapted for actuation only by load current and oltage changes, and means connected to both oad circuit and control means for compensating n said control means for current changes in said oad circuit, whereby said control means functions mly on voltage changes in said load.

5. In combination, an electric power source. a load circuit adapted to include a load connected to said source, a voltage actuated unit, connections from said load circuit at said load to said unit for transmitting load voltage change to said unit, and means for compensating in said unit for voltage change due to current change in said load circuit, said means includinga'current transformer connected to the load circuit, rectifying means for said transformed current, and means for adjusting the magnitude of compensation of said compensation means.

6. In combination, an electric power source, a load circuit connected to said power source and subject to voltage and current change while su ply of power is being delivered thereto from said source, a control element connected to said load circuit and actuated by load voltage change, current change cutout means connected to said pontrol element and to the load circuit for disconnecting saidload and source on occurrence of load voltage change. and compensating means connected between said load circuit and control element effective to compensate in said control element only for current variations in said load circuit, said compensating means comprising a current transformer connected to the load circuit and control element, and voltage change means connected to the transformer and control element for translating current change in said transformer to voltage change in said control element.

' HERBERT DOANE VAN SCIVER, II.

REFERENCES CITED The following references are of record in the file or this patent:

UNITED STATES mm 

